Bicycle Mechanics - Crank length on juvenile bike with 24" wheels

I wasn't sure if I should post this in classic bikes or here.

I found a classic Ralleigh 3-speed bike. It is a kid's bike with 24" wheels. I can fit on it, maybe a couple more inches of seat post would help. But the cranks are quite short, making for a difficult ride.

The cranks appear to be bolted on and so I thought perhaps I could replace them if I could find some cranks that could bolt in the same way.

My question is, if I put longer crank arms on, would the bike become unsafe to ride? Would I risk snagging the pedals when I rounded corners? How much clearance does there need to be between the pedal in the down position and the ground? Or am I worrying needlessly?

You are not worrying needlessly - pedal strike in corners will be a real possibility and a source for added danger and excitement - if that's what you are into.

I look at this as just one more reason why your project is a bad idea - the main reason is that, judging by your comment about getting a longer seatpost, the bike does not fit and was nto designed to fit an adult - even a short adult.

There are literally tens of thousands of old Raleighs sitting quietly in people's garages all over the Western world, and the Women's step-through frame models are as common as the men's, in my experience. I'll bet if you put a WTB ad on your local Craigslist looking for old Raleighs you will get a few responses... There will likely be Raleigh Sportses, Superbes or (if you are lucky) Twentys (20" wheel FOLDING!!!!)

If you are determined to go forward with the kids bike, good luck, and watch that pedal strike - you may wind up on your arse in the middle of an intersection at a very inopportune time.

It would help us to give you good advise if you give us some hard numbers first. What is your true inseam? How long are the cranks? Just how much seatpost extension are you talking about? Oh, and what is the seat tube angle on this bike? This one is a little harder to work out but tell us what you can. If this is a compact frame with a not too long seat post or an old frame with a really short seatpost then fitting a longer seatpost is fine. At a guess this 24" bike will have 152mm(6") cranks on it and if your someone 5' 2" tall then they will fit just fine and I would leave them on.

Some hard numbers please.

Anthony

+1 Bad idea, lots of Raleighs out there. Find one that fits. You will be happier with it for sure.

Ok, I measured everything.
Cranks: 140mm
Approx 125mm from the current pedal to the ground, or 4 and 3/4 inches approx.
I need about 1 inch more seat post plus maybe another inch or two inside for stability.
I have a 30" inseam.

I suppose there are other Raleighs out there. I found this one and it's in pretty good shape. I was hoping to get some use out of it if possible.

The cranks seem to be about right for that bike. Don't recommend anything longer as you will run into problems on corners. As for seat post, always have it in at least as far as the minimum insertion line. That will be at least a couple of inches and usually more. Longer posts are available if yours isn't long enough but, as others said, it sounds like this bike doesn't fit you.

I guess I'll try to sell it. I tried once before but got no response. Maybe someday I'll find a bigger raleigh. I found this one along with a much larger raleigh that was too big for me. It also had coaster breaks which I hate. People in my neighborhood just leave bikes out on purpose.

Ok, I measured everything.
Cranks: 140mm
Approx 125mm from the current pedal to the ground, or 4 and 3/4 inches approx.
I need about 1 inch more seat post plus maybe another inch or two inside for stability.
I have a 30" inseam.

I suppose there are other Raleighs out there. I found this one and it's in pretty good shape. I was hoping to get some use out of it if possible.

OK, numbers help. 140mm cranks are short but for a 30" inseam I reckon they're just a tiny bit short and not unusable. I recommend that cranks should be between 19% to 20.5% of inseam. For you 140mm is just a tiny bit under 19% of inseam. I think you can use them although I think some 152mm cranks would be ideal for you. Based on 125mm of pedal clearance I think you can fit 152mm cranks. I feel that 100mm of pedal clearance is good. I'm guessing the cranks fitted are cotter pin cranks. They are rare these days but you can still find them if you look. There should be someone on eBay who's selling some.

It will take a little work and some time scavenging for parts but I think you could make a nice bike out of it that will fit you well.

Anthony

Ive got a couple of Raleigh Phasers. I built one up to be a MTB and another to be a BMX styled bike.
I had a Raleigh Clipper when I was young and wanted another.
They have a 15" frame. Originally came with 24X1 3/8" wheels.
But I changed to MTB wheels with 24X175 tyres on the Gold bike and too wide, even though Ive swaged the frame, 24X195 on the silver bike.
I have 170 cranks on both. Not had ground clearance problems on them. Ive done a lot of miles on Goldbike. A lot of offroading. Im 5 foot 8inch or 1.7metre tall. I do find they are a bit cramped to ride. Seats high enough but bars need further away.
http://i29.photobucket.com/albums/c296/Alecw35/silverandgold.jpg
Only time I had ground clearance issues on that bike
http://i29.photobucket.com/albums/c296/Alecw35/goldbiketrunk.jpg

Ive got a 26" wheeled version of that bike. But the frame seems the same dimensions and geometry.

Ive got a rat problem in my garage. They chewed the ski grips on silver bike, and the grips and computer buttons on Gold bike. :( So I put a few bikes out in my back yard, roped and wired together. The kids couldnt steal the bikes quickly. So they took the saddles from Gold bike and 2 others.

Unless you are absolutely enthralled with 3-speed Raleighs, I'd look for a small frame hybrid. My daughter and daughter-in-law are 5'1" or 5'2" respectively and comfortably ride Trek hybrids with 15" frames and 700c wheels. These are 3x7-speed GripShift bikes and similar bikes should be readily available at low cost on Craigs List.

A 24" Raleigh will give you problems finding parts due to threading and other incompatibilities with newer components.